We do not know who he is. We do not know where he is. We know only one thing: that he is more prepared than we are. Indeed, he is preparing right now. He is buying his guns. He is accruing his arsenal. The grudges of a lifetime are coalescing into a delusion, and the delusion is articulating itself into something like a plan. In two months, or two weeks, or two days, the plan will be all that he thinks about, and the pressure will become unbearable. He likes to be alone, but his plan needs people, and before too long he will seek out a place where they gather. It might be a school, or a crowded theater. It might be Times Square.

If he lives in Queens, and if he started his journey in, say, Pakistan, we will call him a terrorist, and have a reasonable chance of stopping him before he kills anyone. If he lives in an American town instead of an American city, and started his journey in his American bedroom, we will call him a "shooter" and we have almost no chance of stopping him at all. We will only find out about him after he has turned his geographic particulars into a nightmarish shorthand — "Aurora," "Tuscon," and, of course, "Columbine" — and after the horror he unleashed has been doubled by our helpless knowledge that it fell within a rhythm of horrors, nearly a schedule of horrors, with many more yet to come.

It is now a week after "Newtown," the most horrible of all, and the knowledge that the "lone gunman" — that stock American character — was not really alone at all but rather part of a breed is all that we know of him, our only certainty. He may as well have been part of a confederation, for as he had forebears, he will also have successors. And yet this knowledge remains existential, not operational, and translates to dread instead of action. If the massacre of innocents at Sandy Hook Elementary had been perpetrated by an immigrant with jihadist ties, and if we knew that his example had inspired another immigrant just like him — an immigrant working even now to replicate and even top the toll of tiny bodies — we would demand that heaven and earth be overturned to stop him, and them. But since the massacre was perpetrated by a young American man, white and suburban, "other" only in his alleged autism and painful singularity, we respond in the most American way possible, with an outcry that will turn into a political debate, and a political debate that will turn, as all our debates do, into a recitation of our inalienable rights.

And so yesterday I called New York City Police Commissioner Ray Kelly with a question that today surfaced in the New York Times. Over the last ten years, the NYPD has mobilized to stop "lone actor" terrorists before they strike, and a city of eight million potential "lone actors" has not endured the outlier attack that once seemed inevitable. I wanted to know if the United States could profit by treating "shooters" as "terrorists," and if the methods used by the NYPD to anticipate attacks by disaffected young men with political motivation could be used to anticipate attacks by disaffected young men with psychological motivation — if what we've learned to stop "them" could be marshaled to stop, well, us.

As it turns out, the NYPD has a name for the Adam Lanzas of the world. "We call them 'active shooters,'" Commissioner Kelly told me. "We did a study back in 2002, and came up with a 200-page book about how to deal with them."

The approach outlined in the NYPD's 200-page book on dealing with active shooters turns out to be pretty simple: kill them. But it's also the kind of "reactive" approach that has already proven incommensurate to the threat of terrorism, where a reactive approach is by definition a failed one. When dealing with the threat of terror, the NYPD has reoriented itself in order to be "predictive," and to stop attacks before they happen. It has turned itself into something like a domestic intelligence agency and has used not only undercover agents and confidential informants, but also Internet surveillance and data mining. Over the last six months, it has, according to Kelly, hired "big data" specialists to analyze the vast troves of information now available to law enforcement, and to translate irregularities into interventions.

"We are now using intelligence to try to stop shooters before they strike," Kelly says. "We are going to the Internet and using certain keywords, things like that. The idea is to find out who they are, and refer them for help — preemptive help."

This part is the gist of the Times story. But in our conversation, Kelly went further and made it clear that it's not going to be easy: The problem is that what works for terrorists doesn't necessarily work for active shooters, and for an unexpected reason:

"We know less about people now."

Of course, Kelly was not speaking of people in general. Law-enforcement agencies know more about people now than ever before, thanks to the voluntary and involuntary loss of privacy hastened by the Internet. He is speaking of mentally-ill people, who have found the loophole in the surveillance state: patient confidentiality.

"We are the agency of first and last resort when it comes to mental problems," Kelly says. "We get 80,000 'emotionally-disturbed person' calls a year." But the information that would allow law-enforcement to anticipate the emergence of an active shooter is "hard to get," and is likely to remain so. "There is just very little data available, and the laws that would change that are, if anything, going in the opposite direction, because the advocacy community is so well-organized, so smart, and so sensitive to issues like this."

It is not simply — or even primarily — a matter of emotionally- and mentally-disturbed people being protected by rules of non-disclosure. It is that the kind of disturbed person who might turn into an "active shooter" manages to remain what law enforcement fears and abhors: an exception. "We know a lot more about terrorists than we do about these individuals," Kelly says. "We know what terrorists want to do and how they want to do it. And generally, they're talking to someone, in some way, shape, or form. They're talking to someone or they're going on the Internet. And that's our entry point. If they weren't talking, it would be more difficult for us. Well, lone shooters aren't talking. They're doing it alone."

What a shooter has, then, is not just an arsenal, not just an assault rifle and a stockpile of ammunition. What a shooter has is what Americans, by and large, have lost: privacy, with freedom from their own footprints. The Internet, often portrayed as a loner's paradise, actually exerts a social pull, even to those with anti-social inclinations, and those who manage to resist it present law-enforcement officials like Ray Kelly with the threat they're not prepared to handle: that of radical solitude. Fortunately, Kelly works in New York City, where solitude is hard to come by, and where there has not been a mass shooting of the kind that comes with its own geographic shorthand. Unfortunately, Adam Lanza lived in Newtown, Connecticut, where even though he lived with his mother, he was very much alone.